Up to now, there is known, as a method of injecting working fluid of a fluid dynamic pressure bearing that is used for a recording medium driving device etc., a method disclosed in, for example, Patent Document 1.
The method for injecting working fluid disclosed in Patent Document 1 is a vacuum injection method, wherein a bearing unit, in which an annular cavity having a capacity equal to an appropriate amount is formed at an open end of a gap between a housing and a shaft, is brought to a decompressed state so as to exhaust air from the inside of the bearing unit; a working fluid is dropped into the cavity in the decompressed state and stored therein; and thereafter, the decompressed state is released so that the stored working fluid is injected into the gap of the bearing unit by utilizing the difference in pressure between the inside and the outside of the bearing unit.
In this injection method, since it is necessary to drop a working fluid accurately into a very small region between the housing and the shaft, the working fluid is dropped using a dispenser having a slender tubular injection nozzle.
Patent Document 1:
Japanese Unexamined Patent Application, First Publication No. 2002-174243 (page 3, FIG. 1, etc.)